Prediction of a Ca(BH4)(NH2) quaternary hydrogen storage compound from first-principles calculations

Abstract

We use a combination of density functional theory (DFT) calculations, and a Monte Carlo based crystal structure prediction tool, the Prototype Electrostatic Ground State (PEGS) method, to search for new hydrogen storage compounds in the Ca based mixed amide-borohydride quaternary system. We predict the existence of a new ordered quaternary compound, CaBNH 6 , whose stoichiometry comes from a 1:1 mixture of Ca(BH 4 ) 2 and Ca(NH 2 ) 2 . Our DFT calculations show that CaBNH 6 is ~12.5 kJ/mol Ca (at T = 0 K) lower in energy than the mixture of 1/2[Ca(BH 4 ) 2 + Ca(NH 2 ) 2 ]. DFT phonon calculations of vibrational thermodynamics show that this stability of CaBNH 6 [with respect to Ca(BH 4 ) 2 and Ca(NH 2 ) 2 ] persists to finite temperatures. The predicted crystal structure contains two formula units of CaBNH 6 . We have also performed a thermodynamic analysis of hydrogen decomposition of our predicted compound using the Grand Canonical Linear Programming (GCLP) method combined with a large database of DFT energies and vibrational thermodynamics. We find that the thermodynamically preferred decomposition reaction for CaBNH 6 involves formation of BN with a low decomposition enthalpy. Though the decomposition enthalpy is low, the kinetic behavior of CaBNH 6 decomposition is not yet known. We assert that further experimental investigation of this system is warranted to verify the existence of predicted quaternary compounds in this Ca-B-N-H system, as well as to elucidate their hydrogen release reaction pathways.3

Exploring the High-Pressure Materials Genome

“…E(V 0 ± dV ) can be calculated by minimizing the free energy of the system at the target composition and volume. Grand canonical linear programming (GCLP) (32) techniques using efficient linear solvers are routinely employed to calculate phase stabilities and equilibrium reaction pathways at 0 K and 0 GPa (33)(34)(35)(36)(37). In this work, in addition to the average composition of the system being constrained to that of P, the volume is constrained to V 0 ± dV during energy minimization.…”

Promoted hydrogen release from 3LiBH4/MnF2 composite by doping LiNH2: Elimination of diborane release and reduction of decomposition temperature

“…As compared to 91.1 kJ mol À1 for an undoped 3LiBH 4 /MnF 2 composite[15], the decomposition activation energy of 91.0 kJ mol À1 for a 5 wt.% LiNH 2 -doped 3LiBH 4 /MnF 2 composite indicates that doping LiNH 2 yields no obvious improvement in decomposition kinetics. Considering that doping TiF 3 improves decomposition kinetics significantly but provides little help for the suppression of B 2 H 6 emission in our previous report on a TiF 3 -doped 3LiBH 4 /MnCl 2 composite[16], co-doping LiNH 2 and TiF 3 are underway to further improve the hydrogen storage performance of transition metal borohydrides in terms of both thermodynamics and kinetics.On the basis of experimental results above, we propose a possible mechanism to explain the role of LiNH 2 in the improvement of decomposition properties. First, an amorphous MeBeNeH phase is formed during the doping process.…”

High‐Throughput Computational Screening of New Li‐Ion Battery Anode Materials

“…Grand canonical linear programming72 is a very efficient approach to determining stable reaction pathways for very large sets of compounds, by utilizing extremely fast linear programming routines. This technique was originally developed for predicting hydrogen storage reaction pathways,51, 56, 57, 73; however, the formalism is completely general and here we apply it to lithiation reaction chemstries. GCLP has been previously used by Mason74 et al to do a similar search for lithium battery materials in the Li‐Mg‐B‐N‐H system.…”